The present invention relates to multi-aperture projection displays and single image generation for the same.
So far, no satisfying technical solution exists for mapping different patterns onto different geometries or projection distances. Some solutions enable these mapping characteristics by changing the object structures, such as in the form of a digital imager, or by mechanical manipulation of the mapping optics according to the mapping equation, such as by changing the focal length or back focal length. However, such solutions are expensive.
A specific case of the just described mapping characteristics is maintaining a fixed light pattern across a defined distance range. This characteristic is equivalent to the depth of focus in optics.
The screen-side depth of focus (DoF) of a projector results, according to geometric considerations, from projection distance L, pupil expansion D and the acceptable blur angle β according to FIG. 13 by the following relation (W. J. Smith, Modern Optical Engineering (McGraw-Hill, 2007)).
                              L                      N            ,            F                          =                                            D              ·              L                                      D              ±                              2                ⁢                                  L                  ·                                      tan                    ⁡                                          (                                              β                        2                                            )                                                                                                    ≈                                    D              ·              L                                      D              ±                              L                ·                β                                                                        (        1        )                                Dof        =                                            L              F                        -                          L              N                                ≈                                    2              ⁢                              DL                2                            ⁢              β                                                      D                2                            -                                                L                  2                                ⁢                                  β                  2                                                                                        (        2        )            
Thus, increasing the depth of focus for a given distance L and an accepted blur angle β according to (1) and (2) is only possible by reducing the pupil size D. This is accompanied by brightness loss of the projection, since the transmitted light flux is proportional to the accepted solid angle of each object point in the plane and is thus also reduced when reducing the pupil area D2 (W. J. Smith, Modern Optical Engineering (McGraw-Hill, 2007)).
An alternative approach for obtaining a great projector depth of focus is the usage of laser-illuminated MEMS mirrors using a scanning image buildup. Due to the small mirror area, the same do inherently have a great depth of focus, however, for a good image impression, the same necessitate both coherent light sources and fast, movable mechanical members (MEMS mirrors), which limits their robustness and potential fields of application. Further, the projection image generated in this manner can be adversely influenced by coherent effects, such as speckle, as long as no further technical measures for minimizing the same are taken.
FIG. 14 shows a multi-aperture arrangement of micro-projectors, i.e., an array projector described, for example, in DE 102009024894 A1. The multi-aperture approach used therein allows decoupling the system installation length of the projection system from the obtainable light flux, allowing compact and, at the same time, bright projection systems. Previous publications concerning this optics approach describe a regular two-dimensional arrangement of micro-projectors, each consisting of a field lens 902, an object structure/slide 903 and projection optics 904. The overall arrangement is backlit by an extended or planar light source 901. The projected overall image results from the focused superposition of all single images at a precise projection distance L. This is performed by a well-defined arrangement of the individual slides 903 with regard to the corresponding project lenses 904 according to equation (3).
                              L          =                      s            ·                          p                              Δ                ⁢                                                                  ⁢                p                                                    ,                                  ⁢                  s          =                      FL                          L              -              F                                                          (        3        )            
Here, p means the center aperture distance between the individual projection lenses 904 and p+Δp means the center distance between the object structures or single images 903. For the common sizes, reference is made to FIG. 15, which shows that s is the image distance, i.e., the distance between single image 903 and respective projection optics 904 and F is the focal length of the projection optics 904.
Due to the small apertures of each individual projection lens 904, the depth of focus of the individual projectors is very large (cf. equation (2)). Here, the hyperfocal distance of the individual projections is typically significantly below the distance L.
The set distance where the overall image results by superposition of all single images is essentially determined by the focal length/back focal length of the individual projectors 904 and the center distance difference Δp of the object structures 903 with respect to the corresponding projection lens array of lenses 904 (cf. Marcel Sieler, Peter Schreiber, Peter Dannberg, Andreas Bräuer, and Andreas Tünnermann, “Ultraslim fixed pattern projectors with inherent homogenization of illumination,” Appl. Opt. 51, 64-74 (2012)).
Thus, in equation 3, F corresponds to the focal length and p to the distance or center distance of the projector lenses 904 to one another and Δp to the center distance difference between the slides 902 and the lenses 904, wherein s describes the back focal length resulting according to the paraxial mapping equation by combining L and F. From equation 3, it results that the depth of focus of the overall image 905 projected by superposing the individual micro-projectors, by neglecting geometric aberrations, corresponds to the one of a classical single channel project having a pupil size corresponding to the lateral expansion D of the micro-projector array (cf. Marcel Sieler, Peter Schreiber, Peter Dannberg, Andreas Bräuer, and Andreas Tünnermann, “Ultraslim fixed pattern projectors with inherent homogenization of illumination,” Appl. Opt. 51, 64-74 (2012)).
FIG. 16 shows, for example, the blur behavior of a conventional single channel projector as shown exemplarily in FIG. 13, namely at reference number 906, and a single projector lens and an array projector according to FIG. 14 and FIG. 15 at 908. All systems are focused onto a set distance of 533 mm. The blur behavior of an individual projection channel and an array projector correspond to one another insofar that they are commonly represented by the curve 908. This means that the blur behavior of a single channel projector and a conventional array projector of the same pupil size correspond to one another by neglecting further aberrations and vignetting effects by dead zones.
It would be desirable to have a system enabling the display of different images on different projection distances or geometries in a more objective manner.